Control plane and data plane of a network device may be separated from each other in a software defined network (SDN) structure, so as to flexibly control network flow. Correspondingly, an SDN network may consist of an SDN network device (such as a switch device) and an SDN controller, which are connected with each other through an SDN protocol channel.
As an example of the SDN standard, OpenFlow has been increasingly approved by market. An OpenFlow controller and an OpenFlow switch device may communicate with each other through an OpenFlow channel. The OpenFlow controller may generate a flow table and issue the flow table to the OpenFlow switch device, based on a user-configured or dynamically running protocol. And then, the OpenFlow switch device may process packets, based on the flow table issued by the OpenFlow controller.
Sometimes, OpenFlow switch devices devices at the edge of the SDN network may be connected with some ordinary switch devices, which do not employ the OpenFlow technologies. The ordinary switch devices may operate according to a regular layer two forwarding scheme, rather than according to SDN. Hosts of such ordinary switch devices, are servers, client devices or virtual machines (VMs) which access the network through the ordinary switch device. For example, a host may be a server, client device or a virtual machine on a server connected to the ordinary switch device.